Associated Press photoRepublican Massachusetts gubernatorial candidate Charles D. Baker, left, and state Sen. Richard Tisei, right, face reporters outside the civic center in Wakefield, Monday morning after Baker announced Tisei as his running mate against incumbent Gov. Deval Patrick during an earlier news conference.This is a 1:45 p.m. update of a story posted at 1:10 this afternoon.

BOSTON – Gubernatorial candidate Charles D. Baker followed a Massachusetts Republican tradition on Monday by selecting a veteran state legislator to be his running mate in next year’s election.

Baker, the former Harvard Pilgrim Health Care president, tapped Sen. Richard Tisei as his ally for a primary against fellow Republican Christy P. Mihos. The winner faces the Democratic incumbent, Gov. Deval L. Patrick, and state Treasurer Timothy P. Cahill, who is running as an independent, in the November 2010 general election.

“Throughout his career in public service, Richard has built a solid voting record as a fiscal conservative and a reformer of state government,” Baker said in a prepared statement issued as he appeared with Tisei.

Tisei, a longtime legislator from Wakefield but largely unknown outside the state’s anemic GOP circles, labeled Baker “the right person at the right time to get us out of this mess.”

“Charlie and I share the same philosophy: We understand that the economy needs to be jump-started to get people back to work, that we need to change the business-as-usual attitude on Beacon Hill, and that we need to make Massachusetts more competitive and more affordable,” he said.

Tisei, who owns a real estate company in Lynnfield, is the most veteran Republican in the Senate, have first won election in 1984 at the age of 22. Now 47, he served six years in the House before winning the first of 10 consecutive two-year terms in the Senate.

While describing himself as a fiscal conservative, Tisei is considered a social liberal. He revealed last week that he is gay, and he has supported efforts to legalize gay marriage in Massachusetts. Baker recently revealed his brother is gay, and he has been a longtime supporter of gay marriage.

Such a blend of fiscal conservatism and social liberalism is reminiscent of the formula William F. Weld successfully used to win his 1990 and 1994 gubernatorial campaigns.

Baker’s selection of Tisei has practical implications for both men.

By announcing their campaign now, they can hold joint fundraisers both this calendar year and next, allowing them to seek the maximum $500 annual contribution from individuals in the six weeks remaining in 2009 and during the 11 months next year before Election Day.

They also can also tap their individual networks to funnel $5,000 individual contributions to the Massachusetts Republican Party, whose members and apparatus have largely shunned Mihos after he staged an independent campaign against the GOP’s nominee, Lt. Gov. Kerry Healey, in the 2006 gubernatorial race.

Baker and Tisei can also split campaign appearances across the state, and Tisei can help Baker with his outreach and intelligence in the Statehouse.

Baker formerly worked in state government under Weld, who tapped then-state Sen. Paul Cellucci to be his running mate for the 1990 gubernatorial race. That launched a 16-year rein for GOP control over the Corner Office that continued as Weld and Cellucci won re-election in 1994. Cellucci tapped another state senator, Jane Swift, as his running mate in 1998. In 2002, W. Mitt Romney picked Healey, a former state House candidate and Massachusetts Republican Party leader, as his running mate on a successful gubernatorial ticket.

All four former Republican governors recently endorsed Baker over Mihos.

Under Massachusetts law, candidates for governor and lieutenant governor run separately through the primary; the winners are paired on the general election ballot. By expressing a preferred running mate, gubernatorial candidates can shape the field of lieutenant governor candidates.

In 2006, the Democrats had a contested primary for lieutenant governor, and Patrick ended up paired with Timothy Murray, of Worcester. They are now running for re-election as a tandem, and Murray has far outraised Patrick. Similarly, Tisei ended 2008 with $100,000 in his campaign account. He could spend that money in a way that benefits the campaigns of both him and Baker.

Baker had a small field from which to work has he surveyed potential running mates. There are only five Republicans in the state Senate and 16 in the Massachusetts House.

One prominent Republican, state Sen. Scott P. Brown, is already running in the special election to succeed the late Sen. Edward M. Kennedy. Healey passed on the Senate race for family reasons, and Romney is making moves that would allow him to run for president again in 2012.